The Role of Ascorbic Acid in the Process of Azo Dye Degradation in Aqueous Solution.

In this work, the role of ascorbic acid in the process of azo dye degradation was explained. For this purpose, the kinetics of azo dye degradation under different conditions was studied. Among them, the influence of daylight protection/exposition, different concentrations of ascorbic acid (0.567-0.014 mol/dm3), and temperature (20 °C and 50 °C) on the rate of the dyes' degradation was considered. For this process, the kinetic equation was proposed, which indicates that the process of azo dye degradation using ascorbic acid is first order. Moreover, the observed rate constants were determined, and the mechanism of azo dye degradation was proposed. Spectrophotometry results, together with FTIR, fluorescence spectroscopy, and DFT calculations, explain the origin of the decolorization of the azo dyes and highlight the role of ascorbic acid in this process. Detailed analysis of the obtained products indicates that the process itself goes through several stages in which equally or more toxic compounds are formed. Obtained results from LCMS studies indicate that during tropaeolin OO degradation, 1,2-Diphenylhydrazine (m/z 185.1073) is formed. Thus, the process of azo dye degradation should be carried out in protective conditions. The proposed mechanism suggests that ascorbic acid at high content levels can be used for azo dye degradation from aqueous solution and can be an alternative method for their removal/neutralization from waste solution but with caution during the process.

Tropaeolin OO as a Chemical Sensor for a Trace Amount of Pd(II) Ions Determination.

The selective determination of metals in waste solutions is a very important aspect of the industry and environmental protection. Knowledge of the contents and composition of the waste can contribute to design an efficient process separation and recovery of valuable metals. The problematic issue is primarily the correct determination of metals with similar properties such as palladium and platinum. Thus this paper focuses on the development of a selective method that enables Pd(II) determination in the presence of Pt(IV) ions using the azo-dye tropaeolin OO (TR). For this purpose, the process of the metalorganic complex formation and Pd(II) ions determination were studied by using UV-Vis spectrophotometry under different conditions: solvents (water and B-R buffer), pH (2.09-6.09), temperature (20-60 °C), anions and cations concentrations. The formed metalorganic complex between Pd and tropaeolin OO allows for distinguishing Pd(II) ions from both platinum complexes, i.e. Pt(II), Pt(IV). Moreover, the proposed method can be applied to solutions containing both chloride and chlorate ions. The obtained characteristic spectrum with two maxima allows the determination of palladium even in the presence of other cations (Na, K, Mg, Zn, Co, Ni, Al) and changed concentrations of Pt(IV) ions. Furthermore, the developed spectrophotometric method for the Pd(II) ions determination using tropaeolin OO is characterized by high selectivity towards palladium ions.

Opportunities and Challenges in the Synthesis of Noble Metal Nanoparticles via the Chemical Route in Microreactor Systems.

The process of noble metal nanoparticle synthesis is complex and consists of at least two steps: slow nucleation and fast autocatalytic growth. The kinetics of these two processes depends on the reductant "power" and the addition of stabilizers, as well as other factors (e.g., temperature, pH, ionic strength). Knowing these parameters, it is possible to synthesize materials with appropriate physicochemical properties, which can be simply adjusted by the type of the used metal, particle morphology and surface property. This, in turn, affects the possibility of their applications in various areas of life, including medicine, catalysis, engineering, fuel cells, etc. However, in some cases, the standard route, i.e., the chemical reduction of a metal precursor carried out in the batch reactor, is not sufficient due to problems with temperature control, properties of reagents, unstable or dangerous intermediates and products, etc. Therefore, in this review, we focused on an alternative approach to their chemical synthesis provided by microreactor systems. The use of microreactors for the synthesis of noble metal nanomaterials (e.g., Ag, Au, Pt, Pd), obtained by chemical reduction, is analyzed, taking into account investigations carried out in recent years. A particular emphasis is placed on the processes in which the use of microreactors removed the limitations associated with synthesis in a batch reactor. Moreover, the opportunities and challenges related to the synthesis of noble nanomaterials in the microreactor system are underlined. This review discusses the advantages as well as the problems of nanoparticle synthesis in microreactors.

Waste for Product-Synthesis and Electrocatalytic Properties of Palladium Nanopyramid Layer Enriched with PtNPs.

The presented research is the seed of a vision for the development of a waste-for-product strategy. Following this concept, various synthetic solutions containing low concentrations of platinum group metals were used to model their recovery and to produce catalysts. This is also the first report that shows the method for synthesis of a pyramid-like structure deposited on activated carbon composed of Pd and Pt. This unique structure was obtained from a mixture of highly diluted aqueous solutions containing both metals and chloride ions. The presence of functional groups on the carbon surface and experimental conditions allowed for: the adsorption of metal complexes, their reduction to metal atoms and enabled further hierarchical growth of the metal layer on the carbon surface. During experiments, spherical palladium and platinum nanoparticles were obtained. The addition of chloride ions to the solution promoted the hierarchical growth and formation of palladium nanopyramids, which were enriched with platinum nanoparticles. The obtained materials were characterized using UV-Vis, Raman, IR spectroscopy, TGA, SEM/EDS, and XRD techniques. Moreover, Pd@ROY, Pt@ROY, and Pd-Pt@ROY were tested as possible electrocatalysts for hydrogen evolution reactions.